A strong new earthquake shook Mexico on Saturday, toppling already damaged homes and a highway bridge and causing new alarm in a country reeling from two even more powerful quakes this month that together have killed nearly 400 people.

The U.S. Geological Survey said the new, magnitude 6.1 temblor was centered about 11 miles south-southeast of Matias Romero in the state of Oaxaca, the region hit hardest by a magnitude 8.1 quake on Sept. 7.

It was among thousands of aftershocks recorded in the wake of that earlier quake, the most powerful to hit Mexico in 32 years, which killed at least 90 people.

There was some damage in Oaxaca but no immediate reports of new deaths. The Federal Police agency posted images online showing a collapsed bridge that it said had already been closed due to damage after the Sept. 7 quake.

Bettina Cruz, a resident of Juchitan, Oaxaca, said by phone that the new quake felt "horrible."

"Homes that were still standing just fell down," Cruz said, her voice still shaking. "It's hard. We are all in the streets."

People stand in the street after hearing an earthquake alarm, in Mexico City, Saturday, Sept. 23, 2017. A strong aftershock rolled through Mexico City, Saturday morning, swaying buildings and sending some people running into the street.

(Natacha Pisarenko/AP)

Roberta Villegas, the mother of her missing son Paulino Estrada, left, is embraced by family member Itzel Melendez, as they wait for news outside a quake-collapsed seven-story building where Estrada is believed to be trapped, in Mexico City's Roma Norte neighborhood, Friday, Sept. 22, 2017. Mexican officials are promising to keep up the search for survivors as rescue operations stretch into a fourth day following Tuesday's major earthquake that devastated Mexico City and nearby states.

(Rebecca Blackwell/AP)

Soldiers stand next to a collapsed building where rescue workers race against the clock to reach possible survivors trapped inside a office building in the Roma Norte neighborhood of Mexico City, in the early morning hours of Saturday, Sept. 23, 2017. A 7.1 magnitude earthquake Tuesday toppled more than three dozen buildings in the capital, leaving at least 46 people believed missing in this office building alone.

(Rebecca Blackwell/AP)

People wear dust masks as they watch rescuers work to save people believed to be still alive inside a collapsed office building in the Roma Norte neighborhood of Mexico City, Sept. 22, 2017, more than three days after a 7.1 magnitude earthquake. Hope mixed with fear Friday in Mexico City, where families awaited word of their loved ones trapped in rubble.

(Rebecca Blackwell/AP)

Rescuers race to save people believed to be still alive inside a collapsed office building in the Roma Norte neighborhood of Mexico City, as night falls Friday, Sept. 22, 2017, three days after a 7.1 magnitude earthquake. Hope mixed with fear Friday in Mexico City, where families huddled under tarps and donated blankets, awaiting word of their loved ones trapped in rubble.

(Rebecca Blackwell/AP)

A girl wearing a dust mask covers her face as she watches rescuers work to save people believed to be still alive inside a collapsed office building in the Roma Norte neighborhood of Mexico City, Sept. 22, 2017, three days after a 7.1 magnitude earthquake. Hope mixed with fear Friday as families awaited word of their loved ones trapped in rubble.

(Rebecca Blackwell/AP)

Soldiers stand guard next to a search and rescue operation at a building felled by a 7.1-magnitude earthquake in San Gregorio Atlapulco, Mexico, Friday, Sept. 22, 2017. Inhabitants of the villages that dot the largely rural southern edge of Mexico City said Friday they feel abandoned, as aid and rescue workers focused on the 38 buildings that collapsed nearer the city's downtown in this week's 7.1 magnitude quake.

(Moises Castillo/AP)

A rescue worker uses a machine to break up concrete at the site of an office building felled by a 7.1-magnitude earthquake, in the search for people who are believed to be trapped inside at the corner of Alvaro Obregon and Yucatan streets in Mexico City, Friday, Sept. 22, 2017. Mexican officials are promising to keep up the search for survivors as rescue operations stretch into a fourth day following Tuesday's major earthquake that devastated Mexico City and nearby states.

(Eduardo Verdugo/AP)

Rescue volunteers have a late dinner at a restaurant in Mexico City's La Condesa neighborhood, Friday, Sept. 22, 2017, four days after the 7.1 earthquake. Instead of crowds gathered with beers, small handfuls of rescue workers still dressed in reflective vests took breaks from digging through rubble.

(Marco Ugarte/AP)

Residents, some rescue volunteers, have a late dinner at a restaurant in Mexico City's La Condesa neighborhood, Friday, Sept. 22, 2017, four days after the 7.1 earthquake. The upscale Mexico City neighborhood was one of the hardest hit, with more than a half-dozen collapsed buildings in the immediate vicinity. The few Condesa residents who ventured out Friday night said they were anxious for relief from an anguishing week.

(Marco Ugarte/AP)

Rescue volunteers pose for a photo as they have a late dinner and drinks at a restaurant in Mexico City's La Condesa neighborhood, Friday, Sept. 22, 2017. The long weekâs torment weighing heavy on rescuers and residents alike, several of those gathered Friday night in Condesa said memories of the quake and worries for neighbors and victims were hard to escape.

(Marco Ugarte/AP)

A man drinks a glass of water given to him by a restaurant in Mexico City's La Condesa neighborhood, Friday, Sept. 22, 2017, four days after the 7.1 earthquake. In the stylish Condesa neighborhood young revelers typically spill out from dimly lit bars and restaurants on a Friday night. But the first weekend since the 7.1-magnitude earthquake toppled buildings just blocks away began on a somber note.

(Marco Ugarte/AP)

Rescue volunteers have a late dinner and drinks at a restaurant in Mexico City's La Condesa neighborhood, Friday, Sept. 22, 2017, four days after the 7.1 earthquake. âThe city is still quite tense,â said Israel Escamilla, an engineer, as he sipped a plastic cup filled with Coke at an empty bar. âBut as good Mexicans we have to keep lending support however we can.â

(Marco Ugarte/AP)

Locals play pool at a venue in Mexico City's La Condesa neighborhood, Friday, Sept. 22, 2017, four days after the 7.1 earthquake. The upscale Mexico City neighborhood was one of the hardest hit, with more than a half-dozen collapsed buildings in the immediate vicinity. The few Condesa residents who ventured out Friday night said they were anxious for relief from an anguishing week.

(Nico Gonzalez/AP)

Cruz belongs to a social collective and said that when the new shaking began, she was riding in a truck carrying supplies to victims of the earlier quake.

Nataniel Hernandez said by phone from Tonala, in the southern state of Chiapas, which was also hit hard by the earlier quake, that it was one of the strongest movements he has felt since then.

U.S. Geological Survey geophysicist Paul Caruso said the new temblor was an aftershock of the 8.1 quake, and after a jolt of that size even buildings left standing can be more vulnerable.

"So a smaller earthquake can cause the damaged buildings to fail," Caruso said.

Buildings and street signs swayed and seismic alarms sounded in Mexico City, prompting people with fresh memories of Tuesday's magnitude 7.1 temblor that has killed at least 295 across the region to flee homes and hotels. Some were in tears.

Mexico City Mayor Miguel Angel Mancera told Milenio TV there were "no new developments" due to the quake, though he acknowledged that it provoked "some crises of nerves" among capital residents.

At the site of an office building that collapsed Tuesday and where an around-the-clock search for survivors was still ongoing, rescuers briefly evacuated from atop the pile of rubble before returning to work.

As rescue operations stretched into the fifth day, residents throughout the capital have held out hope that dozens still missing might be found alive.

Officials say the death toll from this week's magnitude 7.1 earthquake in central Mexico has climbed to 305.

More than half the dead — 167 — perished in the capital, while 73 others died in the state of Morelos, 45 in Puebla, 13 in Mexico State, six in Guerrero and one in Oaxaca.

Along a 60-foot stretch of a bike lane in Mexico City, families huddled under tarps and donated blankets, awaiting word of loved ones trapped in the four-story-high pile of rubble behind them.

"There are moments when you feel like you're breaking down," said Patricia Fernandez Romero, who was waiting Friday for word on the fate of her 27-year-old son. "And there are moments when you're a little calmer. ... They are all moments that you wouldn't wish on anyone."

Families have been sleeping in tents, accepting food and coffee from strangers, people have organized to present a united front to authorities, who they pressed ceaselessly for information.

They were told that water and food had been passed along to at least some of those trapped inside. On Friday morning, after hours of inactivity blamed on rain, rescuers were readying to re-enter the site, joined by teams from Japan and Israel. Fernandez said officials told them they knew where people were trapped on the fourth floor.

It's the moments between those bits of information that torment the families.

"It's that you get to a point when you're so tense, when they don't come out to give us information," she said. "It's so infuriating."